Johnson B A, Aswad D W
J Neurochem. 1985 Oct;45(4):1119-27. doi: 10.1111/j.1471-4159.1985.tb05531.x.
The major components of crude brain synaptosomes (synaptic membranes, mitochondria, and myelin) have been separated and analyzed by polyacrylamide gel electrophoresis for the presence of proteins that serve as substrates for protein carboxyl methyltransferase. Of the three fractions, synaptic membranes contain the largest number of individual methyl acceptors (at least seven), while mitochondria contain no well-defined methyl acceptors. Undisrupted myelin contains a single major methyl acceptor with a very low apparent molecular weight. The patterns of protein methylation in synaptic membranes prepared from cerebral cortex, hippocampus, striatum, thalamus, and tectum showed marked differences; however, these differences could largely be explained by differential degrees of myelin contamination in synaptic membranes from the different regions. The effect of trypsin pretreatment on the carboxyl methylation of intact and lysed synaptosomes was studied to estimate the sidedness of the major methylation sites on synaptic membranes. One of the methyl acceptors (Mr 48K) appears to be facing the intracellular surface of the synaptosome, but most sites appear to be outward facing.
粗制脑突触体的主要成分（突触膜、线粒体和髓磷脂）已通过聚丙烯酰胺凝胶电泳进行分离和分析，以检测作为蛋白质羧基甲基转移酶底物的蛋白质的存在情况。在这三个组分中，突触膜含有数量最多的单个甲基受体（至少7个），而线粒体不含明确的甲基受体。完整的髓磷脂含有一种表观分子量非常低的单一主要甲基受体。从大脑皮层、海马体、纹状体、丘脑和顶盖制备的突触膜中的蛋白质甲基化模式显示出明显差异；然而，这些差异在很大程度上可以通过不同区域突触膜中髓磷脂污染程度的差异来解释。研究了胰蛋白酶预处理对完整和裂解突触体羧基甲基化的影响，以估计突触膜上主要甲基化位点的方向性。其中一个甲基受体（分子量48K）似乎面向突触体的细胞内表面，但大多数位点似乎面向外侧。
